Communication systems are well known and comprise many types including land mobile radio, cellular radiotelephone, and personal communication systems to name a few. Within a communication system, transmissions are conducted between a transmitting device and a receiving device over a communication resource, commonly referred to as a communication channel. To date, the transmissions have typically consisted of voice signals. More recently, however, there has been rapidly growing interest in carrying other forms of signals, including high-speed packetized data signals that are suitable for video, audio, and other high bandwidth data applications.
Because of the increase in demand for data communications services, such as Internet services like access to the World Wide Web, the size of data messages and their frequency of transmission have increased and take longer to transfer on existing communication systems. New and/or proposed cellular radio systems, including those based on technologies such as time division multiplexing, frequency division multiplexing, and/or code division multiplexing, allow the data rate available to an individual mobile station to be changed on demand to better accommodate such needs as they arise. This is done in frequency division multiplexed/time division multiplexed systems by allocating a larger number of time division slots and/or carrier (or sub-carrier) frequencies per unit time to the particular user requiring greater throughput. In code division multiple access systems, a greater number of spreading codes are assigned to the user requiring greater throughput.
In such systems, one or more wideband frequency domain channels (having, for example, 50 KHz, 100 KHz, or 150 KHz bandwidths) are subdivided in time and/or code domains into smaller logical channels (some of which can be used for control purposes to dynamically inform the mobile station during operations of the logical channels to be used by the mobile stations). In many systems, the wideband frequency domain channel is first subdivided into narrower frequency domain sub-carriers, which sub-carriers are then similarly subdivided with respect to time and/or codes to yield the desired logical channels.
Unfortunately, when a mobile station, such as a cellular telephone handset, receives, for example, a wide-band time division multiple access (TDMA) transmission on a 100 KHz system, the mobile station is presently required to receive and decode the entire 100 KHz bandwidth of the wideband frequency domain channel to obtain and decode the desired data, regardless of whether the specific assignment for that mobile station only requires receipt of data as carried on a subset of the sub-carriers that constitute the wideband channel. Thus, even if the mobile station is assigned only 50 KHz of the total available bandwidth, the mobile station must nevertheless unnecessarily receive and decode the remaining bandwidth. This results in extra current drain and therefore reduced battery life for a portable device. These circumstances also significantly impact receiver sensitivity as noise contributions that correspond to reception and processing of the full bandwidth channel necessarily impact reception and processing of that portion of the full bandwidth channel that contains the data of interest.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.